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Discrete Sampling EPC Calculations
- Use the statistic (maximum detected concentration or 95UCL) that best aligns with the sample media and applicable toxicity data as the EPC.
- Refer to the EPC Discrete Sampling Guidance for more details.
- For a data set with fewer than eight samples, use the maximum concentration as the EPC, and consider recommending additional sampling.
- For a data set with eight or more samples, with the contaminant detected in at least four samples and detected at least 20 percent of the time, use the appropriate 95UCL as the EPC based on the sample size, number of detects, and data distribution. Refer to the EPC Discrete Sampling Guidance for more details.
- For a data set with eight or more samples, with the contaminant detected in fewer than four samples and detected less than 20 percent of the time, use the maximum detected concentration as the EPC.
Note: ATSDR’s Discrete Sampling Guidance does not apply to all contaminants and types of sampling.
- Refer to Subject Matter Experts (SMEs) when evaluating asbestos and lead.
- Refer to ATSDR’s Toxic Equivalents Guidance for Dioxin and Dioxin-like Compounds for dioxins.
- Refer to ATSDR’s Non-Discrete Sampling Guidance for incremental and composite sampling data.
- Refer to ATSDR’s Guidance for Calculating Benzo(a)pyrene Equivalents for Environmental Samples Analyzed for PAHs for PAHs.
- Refer to the ADS group for EPC guidance when evaluating dependent data. These are instances where the results of one sample at least partially predict the results of another sample.
- You can find all final guidance in the PHAGM Resources section.
Pica is the persistent eating of non-nutritive substances such as dirt or paint. Incidental ingestion of soil occurs in all age groups, particularly in children (who have more hand-to-mouth contact). ATSDR evaluates pica for any possible scenarios that could involve soil/sediment exposures for children and a pica comparison value (CV) is met or exceeded. The following guidance applies for calculating EPCs for soil pica exposures:
- Run a default pica intermediate and acute residential scenario in the PHAST Soil/Sediment Dose Calculator. You will use an EPC that represents the maximum concentration of surface soil that a child could access. The default scenario in PHAST assumes an exposure of three days a week and an intake rate of 5,000 mg/kg for acute and intermediate scenarios.
*If PHAST indicates the default scenario using the maximum concentration exceeds acute and/or intermediate health guidelines (as indicated by a hazard quotient > 1 in PHAST), go to step 2.
- Enter site-specific parameters, if available, in PHAST to determine whether a single pica event is a health concern. Note that site-specific data are not often available and are not required to evaluate this one-time dose. Typically, this one-time dose uses an exposure of 1 day and the default intake of 5,000 mg/kg.
In your documents, report the pica results for all scenarios that you evaluated. Refer to ATSDR’s Discrete Sampling Guidance and ATSDR’s Soil and Sediment Ingestion EDG for more information. You can find these documents in the PHAGM Resources section.
Health assessors will use a software application or programming language to calculate the 95UCL for the EPC. While many different software applications and programming languages are available, ATSDR recommends using the ATSDR EPC Tool. The tool is a web application built to help ATSDR and its partner health assessors calculate EPCs for discrete environmental data during the PHA process. Health assessors can use the EPCs calculated with this tool whenever the 95UCL or maximum value are appropriate metrics for evaluating exposures. Email phast@cdc.gov to gain access to ATSDR’s EPC Tool. Health assessors can get more information in the EPC Tool User’s Guide, available on the EPC Tool Resources page.
- Do not delete non-detect observations from data sets.
- Do not consider non-detect observations with extremely high detection limits.
- Do not replace non-detect observations with a single surrogate value.
- Do not calculate 95UCLs for contaminants with eight to 19 samples and three or fewer detected results.
- Do not calculate 95UCLs for contaminants with 20 or more samples and less than 20% detected results.
- Perform a data quality review.
- Identify and process non-detect observations.
- Identify and process lower-bound concentration data points.
- Identify and process duplicate samples and replicate analyses.
- Plot environmental data to visualize the measurements’ distribution.
Refer to ATSDR’s Discrete Sampling Guidance for more information on the concepts outlined in this section, and on the statistical tools for performing your 95UCL calculations and selecting the appropriate 95UCL based on the characteristics of the dataset. If you use ATSDR’s EPC Tool, many of these rules will automatically be applied.